To determine the relationship between phytoplankton and bacteria biomass near the icewater interface in the Antartic, the seasonal distr~butions of phytoplankton and bacteria populations were investigated on the continental shelf of Terre Adehe durlng the ice coverage period. An under-ice surface station was sampled weekly from March 1991 to January 1992 for the bottom ice and for surface, 0.5 and 2 m depth seawater. Seawater chlorophyll a values ranged from 0.9 my m-"n summer to 0 01 mg m-"n winter. Values 50 times higher were recorded in the overlying ice. Bacterial abundance ranged from 0.5 x 10" cells m -3 in July to 6.0 X 10" cells m-%after the ice break-up. Values reaching u p to 2.5 X 1012 cells nl-"were recorded in sea ice. Bacterial biomass and chlorophyll a concentrations were significantly correlated in both sea ice and underlying seawater Bacterial biomass represents between 1 and 10% of total microbial biomass in sea ice and from 10':,, (summer) to up to 90% (winter) of the living community in the underlying seawater.

The distributions of bacterial populations in sea ice and underlying seawater were investigated on the continental shelf of the "Terre Ad61ie" area. A reference station was sampled weekly from January 1991 to January 1992. In winter, the survey included a minimum of six sampling layers: surface and bottom ice, brine, seawater from the interface, and at 0.5 and 2 m depth. In seawater, the total bacterial abundance range(] from 0.5 x 10 s cells m1-1 in July to 6.0 x 105 cells ra1-1 after ice break. Values reaching 2.5 x 106 cells ral-1 were recorded in the overlying ice cover. Mean cell volumes were twice as high in brine as in seawa'Ler. The saprophytic bacterial abundance ranged from 5.0 x 104 CFU (colony-forming units) m1-1 in some winter interface samples to less than 1.0 x 103 CFU ml -1 in most of the summer seawater samples. In sea ice a clear decreasing gradient for most of the studied bacterial parameters from the surface layers towards the bottom layer was found. The ice cover had a disc,::rnible impact on underlying seawater, but its influence was restricted to a limited interface layer.

No abstract

The dynamics of Antarctic coastal marine bacterioplankton has been studied over a 2-year period. Two field stations were sampled between one and three times a week in 1989 and 1991 in the "Terre Ad61ie" area. The survey included physicochemical (temperature and particulate organic matter) and bacteriological (total and heterotrophic counts, cell volume and frequency of dividing cells estimation) measurements. The results suggest that a strong interannual variability affects the total bacterial abundance, the mean cell volume, the percentage of free living cells and, to a lesser extent, the culturable saprophytic bacterial communities. The observed variability could be partly explained by a large deficit of solar irradiance during the 2nd year of study that may have affected sea ice and seawater primary production.

The distributions of bacterial populations in sea ice and underlying seawater were investigated on the continental shelf of the "Terre Ad61ie" area. A reference station was sampled weekly from January 1991 to January 1992. In winter, the survey included a minimum of six sampling layers: surface and bottom ice, brine, seawater from the interface, and at 0.5 and 2 m depth. In seawater, the total bacterial abundance ranged from 0.5 x 105 cells m1-1 in July to 6.0 x l0 s cells m1-1 after ice break. Values reaching 2.5 x 106 cells mI-1 were recorded in the overlying ice cover. Mean cell volumes were twice as high in brine as in seawater. The saprophytic bacterial abundance ranged from 5.0 x 10 ~ CFU (colony-forming units) m1-1 in some winter interface samples to less than 1.0 x 103 CFU ml -1 in most of the summer seawater samples. In sea ice a clear decreasing gradient for most of the studied bacterial parameters from the surface layers towards the bottom layer was found. The ice cover had a discernible impact on underlying seawater, but its influence was restricted to a limited interface layer.